Summary of Work: HIV-1 reverse transcriptase (RT) is a large, complex multi-functional enzyme required for genomic replication of the virus. The enzyme will be a target for anti-viral therapy in the future, and in the past it has been by far the most successful target for anti-viral therapy. The enzyme is responsible for the extreme genetic hypervariability of HIV-1 and, hence, the virus' ability to escape drug- mediated suppression in AIDS patients via mutation to drug-resistance. Through studies of the RT's mechanism, our laboratory, in collaboration with Dr. Kunkel's laboratory, discovered that the mutation propensity is linked to how well the enzyme stays attached to the template strand during replication. Thus, if RT falls off the viral template strand during replication, it tends to make an error (or mutation)at the point where it climbs back on the template and continues replication. This mechanism appears to account for most, if not all, of the HIV-1 hypervariability. Much insight into the mechanism of "falling off" has been gained recently by combining structural information on RT with biochemical studies of the wild type enzyme and enzymes strategically altered in specific amino acid residues that control affinity of binding to the template. We have localized most of the critical template-binding amino acids of the RT to a very small region near the polymerase active site known as the "Minor Groove Binding Track." This protein motif was first appreciated through molecular modeling conducted by Dr. Darden and Dr. Gorenstein. These studies of the template-binding surface of RT will enable our group and other groups to design drugs that will bind to the enzyme just as tightly as the template and, thus, block the enzyme before it has a chance to begin replication. The template-binding surface on RT is considered to be different from those on the surfaces of the cellular DNA polymerases. Therefore, such new inhibitors of RT should be highly specific to RT, as well as highly effective. Studies of this interesting enzyme also will enhance our understanding of other replicative DNA polymerases.